The experiments described were designed to study the molecular behavior of mitochondrial DNA (its replication, recombination and segregation) during yeast mating so that the relationship between mitochondrial DNA behavior and mitochondrial DNA transmission genetics can be understood. The several proposed experiments will allow the parallel analysis of both the molecular behavior of mitochondrial DNA and the inheritance of mitochondrial genetic markers. These experiments will utilize a synchronous mating procedure for producing large populations of yeast zygotes suitable for studies at the molecular level. To allow study of mitochondrial DNA transmission at the genetic level, each pair of mated parental strains will contain differing mitochondrial genetic markers. The particular parental strains chosen for study represent three classes of yeast mitochondrial phenotypes (grande, neutral petite and suppressive petite). They were chosen because they have unique mitochondrial phenotype transmission patterns and because their mitochondrial DNA's differ markedly in molecular organization. The correlation of the molecular and genetic data obtained from these mating experiments should allow a better understanding of many events upon which mitochondrial inheritance is based.